Beating Heart (OC x SansAU)

Years ago, Wren fell into the underground by mistake. This marked them as an anomaly. However, they fell into a timeline doomed to be reset and Error had made a deal, so he left them alone. Years later, Wren appears again, different, changed, and more powerful. Now, Ink and Error have decided they must capture the anomaly before they have a chance to wreak havoc on unsuspecting AUs. (there is a y/n version of this story!!)